You mention chargers but did not mention how they are the only exception to the splats to kill rule. They have base 40 dmg on uncharged shots, but with 3 main and 2 subs of dmg up, this will increase it to 50.05 dmg; going from 3HKO to 2HKO.
Another important aspect to using dmg ups is the burst bomb. With dmg ups you can combo burst bomb + 1 shot with neo splash, custom jet, splatshot. Burst bombs also have 3 different hitboxes, with enough dmg ups you can combo strongest hitbox + weakest hitbox acting as a sort of pseudo exception to the splat to kill rule as well.